I would like to know how to this to. I tried to put the line of code in my template file, and it crashed the site until I took the line of code back out. I don’t see any settings panel in the dashboard or anything, so I don’t know how to do it either.

get a copy of the function twentytwelve_content_nav( $html_id ), paste it into functions.php (make sure if the file is new, to have <?php in the first line), and edit it to include the code for the plugin;